1. Field of the Art
This invention relates to a process for preparing a resin having five-membered rings and double bonds in its main polymeric chain and having high thermal resistance as well as excellent stiffness and impact resistance.
In petrochemical industries, naphtha obtained from petroleum fractions has been subjected to thermal decomposition to produce olefins such as ethylene and propylene. These olefins have been used for production of chemical materials such as ethylene oxide and acrylic acid as well as resin materials such as polyethylene and polypropylene.
However, almost none of the fractions having 5 carbon atoms which are obtained as by-products in the thermal decomposition of naphtha are being utilized industrially except for isoprene as a starting material for synthetic rubber, and most of these fractions are being consumed as fuel.
2. Prior Art
The content of cyclopentadiene is one of the highest of the components in these C.sub.5 fractions. Also cyclopentadiene has high reactivity, and thus its utilization can be expected to be developed to provide novel products of high added value such as cyclopentane and norbornene derivatives.
Among them, a polymer which can be obtained by subjecting a norbornene derivative monomer to polymerization through ring opening in the presence of a metathesis catalyst containing tungsten or molybdenum is very attractive as a novel engineering plastic. Especially, a possible polymer through ring opening of 5-norbornene-2-carboxylic acid, which is derived from cyclopentadiene and acrylic acid by the Diels-Alder reaction, has the possibility of providing engineering plastics having high heat-resistance because of the carboxylic groups contained therein.
However, it is difficult to cause a monomer such as 5-norbornene-2-carboxylic acid to undergo polymerization through ring opening because of the strong polarity of its carboxyl group. Thus, direct polymerization through ring opening of 5-norbornene-2-carboxylic acid has not been successfully accomplished on an industrial basis.
A process for preparing a polymer through ring opening of 5-norbornene-2-carboxylic acid is proposed in Japanese Laid-Open Patent Application No. 65018/1981 specification, wherein a certain norbornene derivative is converted into the corresponding ester and then is subjected to polymerization through ring opening, which is followed by hydrolysis of the ester groups.
This process, however, comprises dissolving the ester polymer in an organic solvent and hydrolyzing it in one stage by addition thereto of an alkali substance. The polymer resulting from the ring opening has deficient thermal resistance.
As a result of our intensive research directed toward improving the thermal resistance and stiffness of product polymers, we have found that the desired thermal resistance and other characteristics can be markedly improved by carrying out the hydrolysis treatment in two stages.